The present invention relates to a method for forming a metal line in a semiconductor device, and more particularly, to a method for forming a metal line in a semiconductor device, which can easily apply a material for a contact plug into a contact hole.
A semiconductor device includes a plurality of memory cells and a plurality of transistors which are connected with one another by junction areas, contact plugs and metal lines.
Contact plugs transmit the voltages, provided thereto mainly through metal lines, to the gates or the source or drain areas of transistors. For example, in the case where a contact plug is formed between two transistors, the contact plug is formed over a junction area (a source or drain area). The contact plug transmits the voltage, provided thereto through a metal line, to the junction area (the source or drain area). If a transistor is activated, a channel is formed, and the voltage provided to the junction area (the source or drain area) is transmitted through the channel to another transistor.
The contact plug formed over the junction area (the source or drain area) does not contact the gate. An insulation layer is formed between the gate and the contact plug to isolate the contact plug from the gate.
A conventional method for forming a contact plug is described below.
An insulation layer is an oxide-based layer formed on a semiconductor substrate to insulate a transistor formed on the semiconductor substrate. A first insulation layer pattern, in which an area to be defined with a contact hole is open, is formed on the insulation layer. By implementing an etching process using the first insulation layer pattern, the exposed portion of the insulation layer is removed, and a contact hole is defined. The contact hole is filled with a metal layer to form a contact plug. However, an overhang phenomenon, in which the metal layer is quickly formed at the upper end of the contact hole (i.e., at the upper edge of the insulation layer), is likely to occur. If the overhang phenomenon occurs, voids can be formed in the contact plug because the upper end of the contact hole may be closed before the contact hole is completely filled with the metal layer.
If voids are formed in the contact plug, H2O2 used during a subsequent planarization process can leak into the voids, causing damage to the metal layer. Thus, the electrical characteristics of a semiconductor device can be degraded.